Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
  • C01B15/01—Hydrogen peroxide
  • C01B15/013—Separation; Purification; Concentration
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D301/00—Preparation of oxiranes
  • C07D301/02—Synthesis of the oxirane ring
  • C07D301/03—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds
  • C07D301/12—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with hydrogen peroxide or inorganic peroxides or peracids
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
  • C01B15/01—Hydrogen peroxide
  • C01B15/029—Preparation from hydrogen and oxygen
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency

Definitions

• the present invention relates to an integrated process for the preparation in continuous of epoxides by the direct oxidation of an olefin with hydrogen peroxide.
• the present invention relates to an integrated process for the preparation in continuous of propylene oxide consisting in the production of an alcoholic or hydro-alcoholic solution of hydrogen peroxide by the reaction between hydrogen and oxygen in the presence of a bimetallic catalyst based on palladium or platinum as active components, feeding said solution to an epoxidation process of propylene in the presence of an epoxidation catalyst, and feeding the recycled alcoholic solvent leav- ing the epoxidation plant, suitably pretreated, to the hydrogen peroxide production plant.
• the process may comprise a further step (e) , in which the raw hydro-alcoholic mixture of the flash column bottom, is used, when necessary, for diluting the alcoholic or hydro-alcoholic solution of hydrogen peroxide obtained in step (a) to the value re- quired by the epoxidation plant.
• Epoxides, or olefin oxides are intermediates which can be used for the preparation of a wide variety of compounds.
• epoxides can be used for the produc- tion of glycols, condensation polymers such as polyesters or for the preparation of intermediates used in the synthesis of polyurethane foams, elastomers, seals and similar products .
• the commercialized chlorohydrin process involves the synthesis of propylene chlorohydrin (PCH) and subsequent dehydrohalogenation of PCH to propylene oxide (PO) .
• PCH propylene chlorohydrin
• PO propylene oxide
• Processes via oxidation preferably use ter butyl hy- droperoxide and ethylbenzene hydroperoxide as hydro- peroxides. These processes cause the formation of a higher quantity of co-products of commercial interest with respect to PO. For example, the process via ter butyl hydroperoxide co-produces 2.5-3.5 Kg of ter butyl alcohol per Kg of PO, whereas that via ethylbenzene hydroperoxide co-produces 2.2-2.5 Kg of styrene per Kg of PO.
• Aqueous solutions of H 2 0 2 are typically obtained industrially by means of a complex two-step process. In this process a solution of anthraquinone, such as butylanthra- quinone or ethylanthraquinone, in an organic medium immiscible with water, is first hydrogenated and then oxidized with air to produce H 2 0 2 which is subsequently extracted in aqueous phase.
• anthraquinone such as butylanthra- quinone or ethylanthraquinone
• This process is onerous due to the high costs deriving from the investment necessary for setting up the complex production unit, the necessity of separating and disposing of the by-products generated during the oxi- dation phase, and purifying and reintegrating the a thra- quinone solution before its re-use.
• a second method for the production of hydrogen peroxide comprises the use of secondary alcohols such as isopro- panol and ethylbenzylalcohol (US 2,871,102, EP-378,388) or high-boiling secondary alcohols such as diaryl methanol (US 4,303,632) with oxygen.
• secondary alcohols such as isopro- panol and ethylbenzylalcohol (US 2,871,102, EP-378,388) or high-boiling secondary alcohols such as diaryl methanol (US 4,303,632) with oxygen.
• These processes generally use a catalytic system consisting of a noble metal, particularly metals of the platinum group or their mixtures, in the form of salts or as supported metals, by reacting the two gases in a solvent consisting of an aqueous medium or an aqueous-organic medium.
• a catalytic system consisting of a noble metal, particularly metals of the platinum group or their mixtures, in the form of salts or as supported metals, by reacting the two gases in a solvent consisting of an aqueous medium or an aqueous-organic medium.
• Patent application EP-812836 describes a process for the preparation of propylene oxide which consists in reacting hydrogen and oxygen in the presence of a catalytic system based on supported palladium, in a hydro- alcoholic medium and using the hydro-alcoholic mixture of hydrogen peroxide thus obtained in the epoxidation process.
• the illustrative examples of this document describe the production of hydro-alcoholic solutions containing H 2 0 2 in concentrations ranging from 0.15 to 0.39% by weight.
• the Applicant has now found that by using a well defined group of metallic catalysts and operating conditions in the initial reaction between hydrogen and oxygen, by suitably treating the recycled alcoholic solvent leaving the epoxidation plant before being fed to the hydrogen peroxide production plant, and by using the raw hydro- alcoholic mixture of the flash column bottom, when necessary, to dilute the hydro-alcoholic solution of hydrogen peroxide obtained in step (a) to the value required by the epoxidation plant, an overall high process efficiency is obtained in terms of productivity and selectivity.
• the objective of the present invention relates to an integrated process for the preparation in continuous of epoxides by the direct oxidation of an olefin with hydrogen peroxide which comprises:
• step (b) putting the alcoholic or hydro-alcoholic solution of hydrogen peroxide obtained in step (a) in contact with an olefin and a buffering agent, in the presence of an epoxidation catalyst suspended in the reaction solvent, in order to obtain a reaction mixture containing the epoxide corresponding to the olefin, water and the alcoholic solvent;
• step (c) treating the alcoholic stream leaving step (b) , after separation of the epoxide, in order to eliminate the nitro- genated compounds present; (d) feeding the alcoholic solvent obtained in (c) to step
• the process may comprise a further step (e) , wherein the raw hydro-alcoholic mixture of the flash column bottom, is used, when necessary, for diluting the hydro-alcoholic solution of hydrogen peroxide obtained in step (a) to the value required by the epoxidation plant. This advantageously allows a reduction in the volume of solvent to be distilled in the epoxidation reaction plant.
• the process for the synthesis of epoxides comprises: (a) feeding to a reactor, containing a catalyst based on palladium and platinum, heterogeneous and kept in dispersion in a liquid reaction medium:
• a liquid stream consisting of an alcohol or an alcohol-water mixture with a prevalent alcoholic content, containing an acid promoter and a halogenated promoter.
• a gaseous stream containing hydrogen, oxygen and an inert gas characterized in that the concentration of hydrogen is lower than 4.5% by volume and the concentration of oxygen is lower than 21% by volume, the complement to 100 being an inert gas;
• removing from the reactor: (iii) a liquid stream essentially consisting of the stream (i) and also containing the hydrogen peroxide and water produced by the reaction, characterized in that the concentration of hydrogen peroxide is higher than 3% by weight;
• the reactor used can be any reactor suitable for operating in continuous and conducting the reaction in a tri- phasic system such as that described, obtaining an effective contact between the gaseous phase, liquid phase and catalyst kept in dispersion (so-called slurry system) .
• slurry system a reactor suitable for operating in continuous and conducting the reaction in a tri- phasic system such as that described, obtaining an effective contact between the gaseous phase, liquid phase and catalyst kept in dispersion (so-called slurry system) .
• stirred reactors, bubble reactors, gas-lift reactors with internal or external circulation, such as those described in the state of the art, are suitable for the purpose.
• the reactor is maintained under appropriate temperature and pressure conditions.
• the temperature normally ranges from -10°C to 60°C, preferably from 0°C to 40°C.
• the pressure normally ranges from 1 to 300 bars, preferably from 40 to 150 bars.
• the residence time qf the liquid medium in the reactor normally ranges from 0.05 to 5 hours, preferably from 0.10 to 2 hours.
• the catalyst which can be used for the purposes of the invention is a heterogeneous catalyst containing palladium and platinum as active components .
• the palladium is normally present in a quantity ranging from 0.1 to 3% by weight and the platinum in a quantity ranging from 0.01 to 1% by weight, with an atomic ratio between platinum and palladium ranging from 1/500 to 100/100.
• the palladium is preferably present in a quantity ranging from 0.4 to 2% by weight and the platinum in a quantity ranging from 0.02 to 0.5% by weight, with an atomic ratio between platinum, and palladium ranging from
• metals of group VIII or IB such as, for example, ruthenium, rhodium, iridium and gold, can be present as active components of promoters, in a concentration generally not higher than that of the palladium.
• the catalyst can be prepared by dispersing the active components on an inert carrier by means of precipitation and/or impregnation starting from precursors consisting, for example, of solutions of their salts or soluble complexes, and therein reduced to the metal state by means of thermal and/or chemical treatment with reducing substances such as hydrogen, sodium formiate, sodium citrate by means of preparative techniques well known in the state of the art.
• the inert carrier may typically consist of silica, alumina, silica-alumina, zeolites, activated carbon, and other materials well known in the state of the art. Activated carbon is preferred for the preparation of the catalysts useful for the invention.
• Activated carbons which can be used for the invention are selected from those of fossil or natural origin deriv- ing for example from wood, lignite, peat or coconut and having a surface area higher than 300 m 2 /g and which can reach 1400 mVg, in particular those having a surface area higher than 600 m z /g.
• Preferred activated carbons are those with a low ash content.
• the activated carbon Before the supporting or impregnation of the metals, the activated carbon can be subjected to treatment such as washing with distilled water or treatment with acids, bases or diluted oxidizing agents, for example acetic acid, hydrochloric acid, sodium carbonate and hydrogen peroxide.
• treatment such as washing with distilled water or treatment with acids, bases or diluted oxidizing agents, for example acetic acid, hydrochloric acid, sodium carbonate and hydrogen peroxide.
• the catalyst is normally suspended in the reaction medium at a concentration ranging from 0.1 to 10% by weight, preferably from 0.3 to 3% by weight.
• the liquid stream (i) consists of an alcohol or a mixture of C1-C 4 alcohols or a mixture of said alcohols with water with a prevalent alcoholic content.
• a mixture with a prevalent alcoholic content refers to a mixture containing over 50% by weight of alcohol or mixture of alcohols.
• C 1 -C4 alcohols methanol is preferred for the purposes of the invention.
• preferred mixtures is a mixture of methanol and water containing at least 70% by weight of methanol .
• the liquid stream also contains an acid promoter and a halogenated promoter.
• the acid promoter can be any substance capable of generating H + hydrogen ions in the reaction liquid medium and is generally selected from inorganic acids such as sulfu- ric, phosphoric, nitric acid or from organic acids such as sulfonic acids.
• Sulfuric acid and phosphoric acid are preferred.
• concentration of the acid generally ranges from 0 to 1000 rag per kg of liquid medium and preferably from 10 to 500 mg per kg of liquid medium.
• the halogenated promoter can be any substance capable of generating halide ions in the reaction liquid medium.
• Substances capable of generating bromide ions are preferred. These substances are generally selected from hydro- bromic acid and its salts soluble in the reaction medium, for example alkaline bromides, hydrobromic acid being preferred.
• the concentration of halogenated promoter generally ranges from 0.1 to 50 mg per kg of liquid medium and pref- erably from 1 to 10 mg per kg of liquid medium.
• the gaseous stream (ii) at the inlet contains a concentration of hydrogen of less than 4.5% by volume and a concentration of oxygen of less than 21% by volume, the complement to 100 being an inert gas, which is generally selected from nitrogen, helium, argon. Said gas is preferably nitrogen.
• the concentration of hydrogen preferably ranges from 2% to 4% by volume and the concentration of oxygen preferably ranges from 6% to 18% by volume.
• the oxygen can be supplied to said stream using pure or substantially pure oxygen, or enriched air, as raw material, containing for example from 21 to 90% of oxygen or air, the composition of the stream then being brought to the desired values, defined above, by the addition of a suitable concentration of inert gas .
• the liquid stream (iii) leaving the reactor normally has a concentration of hydrogen peroxide of over 3% by weight and, preferably from 4% to 10% by weight. It also contains the acid promoter and halogenated promoter in quantities equal to those charged with the liquid stream fed and water in a quantity equal to that charged with the liquid stream fed together with the water obtained as reaction by-product. The latter usually represents an addi- tional concentration of 0.5% to 2.5% by weight.
• the liquid stream (iii) is separated from the catalyst by means of filtration techniques well known in the state of the art, for example by the use of filters situated inside the reactor or in a special recirculation cycle of the reaction mixture outside the reactor. In the latter case, the tangential filtration technique can also be conveniently adopted.
• the liquid stream (iii) proves to be stable to storage without requiring the addition of stabilizing substances.
• the gaseous stream (iv) leaving the reactor essentially consisting of non-reacted hydrogen and oxygen and the inert gas, generally contains a volume concentration of hydrogen equal to or lower than 2%, normally ranging from 0.5 to 1.5%, and a volume concentration of oxygen generally less than 18%, normally ranging from 6 to 12%.
• the gaseous stream leaving the reactor is recycled to the feeding to the reactor, after flushing from the system the fraction necessary for eliminating the quantity of in- ert gas charged in excess with the feeding, particularly when air is used as oxygen source.
• the gaseous stream (ii) fed to the reactor consists of the recycled fraction of the above stream (iv) , containing a quantity of hydrogen and oxygen (as such or in the form of air or en- riched air) essentially equal to that used up by the reaction and that used for the flushing.
• the gaseous stream (iv) leaving the reactor is fed to one or more subsequent reactors operating analogously to that described above, after adding each time a quantity of hydrogen and oxygen (as such or in the form of air or enriched air) essentially equal to that used up by the reaction which takes place in the single reactors.
• the possibility of minimizing the concentrations of acid and halogenated promoters present in the reaction liquid medium positively influences the stability of the catalytic system; there are no signs of a substan- tial loss in the catalytic activity after 1000 hours of re- action in continuous .
• the filtered liquid stream (iii) is fed to a reaction unit consisting of one or more reactors containing the epoxidation catalyst suspended in the reaction solvent to- gether with the olefin and a buffering agent.
• the liquid stream (iii) is diluted with the raw hydro-alcoholic mixture of the flash column bottom to the value required by the epoxidation plant.
• the filtered liquid product leaving the reaction unit is fed to a distillation unit consisting of one or more stripping (flash) columns, one for each reactor of the re- action unit, to obtain a product at the head essentially consisting of olefin oxide and non-reacted olefin and a product at the bottom essentially consisting of solvent, non-reacted hydrogen peroxide, water and reaction byproducts.
• the product at the bottom of the distillation unit is fed, for the quota not recycled to the epoxidation reaction unit, to a decomposition unit R4 consisting of one or more reactors containing a decomposition catalyst having the function of decomposing the residual hydrogen peroxide into 0 2 and H 2 0.
• the mixture leaving the decomposition unit R4, essen- tially consisting of solvent, oxygen and water, is fed, together with an inert gas (preferably nitrogen) , to a phase separator V4 to obtain, at the head, a gaseous phase containing oxygen, inert gas and traces of solvent and, at the bottom, a liquid phase consisting of solvent, water and reaction by-products .
• an inert gas preferably nitrogen
• the gaseous phase leaving V4 is fed to a condensation system consisting of one or more condensers in series for the recovery of the residual solvent, whereas the non- condensable compounds (oxygen and inert gas with traces of solvent) are discharged.
• the solvent leaving the condensation system and the liquid phase leaving R4 are fed to the distillation column C6-A together with a diluted aqueous or hydro-alcoholic so- lution containing sulfuric acid (about 10-50 mg/kg of sul- furic acid with respect to the total stream) to obtain, at the head, the purified solvent containing traces of light products and a product, at the bottom, essentially consisting of reaction water and that charged with the hydrogen peroxide, reaction by-products and traces of solvent, which is discharged.
• a diluted aqueous or hydro-alcoholic so- lution containing sulfuric acid about 10-50 mg/kg of sul- furic acid with respect to the total stream
• the solvent leaving the condensation system and the liquid phase leaving V4 are preferably fed towards the bottom of the distillation column C6-A, whereas the acid solu- tion is fed at a height equal to about 2/3 of the column.
• the function of this acid treatment is to completely separate the nitrogenated basic products present in the stream, which could influence the performance of the catalyst used for the synthesis of hydrogen peroxide.
• the solvent leaving the head of the column C6-A is fed to a column C6-B, in order to separate the light products at the head, whereas the purified solvent is separated at the bottom.
• the stream at the head of the column C6-B is sent to a distillation column C6-C, to recover, at the bottom, the solvent without light products, recycled to the hydrogen peroxide synthesis reaction, and a concentrated stream of light products, at the head.
• the acid treatment in the column described above can be substituted by means of treatment on the methanol at the head of C6-A with activated carbon, sulfonic resins or sul- fonated carbons (Italian Patent Application MI 98A01843) .
• the product at the head of the stripping column (s) and the vent products of the reactors are fed to a distillation column C4 to obtain a product, at the head, consisting of non-reacted olefin, recycled to the reaction unit, and a product, at the bottom essentially consisting of olefin oxide.
• the product at the bottom of the distillation column is fed to a purification system C5.
• the residual olefin ob- tained at the head. C5 is recycled to the reaction unit, the liquid phase, at the bottom, essentially consisting of solvent is recycled to the flash column(s), and the olefin oxide with a commercial purity is obtained from a lateral cut in the upper part of the column.
• Olefins which can be used in the process of the present invention are those having general formula (I)
• Ri, R 2 , R3 and R 4f can be hydrogen, an alkyl radical with from 1 to 20 carbon atoms, an aryl radical, alkylaryl radical with from 7 to 20 carbon atoms, a cyclo-alkyl radical with from 6 to 10 carbon at- oms, an alkylcyclo-alkyl radical with from 7 to 20 carbon atoms .
• radicals Ri, R ⁇ , a and R 4 can form, in pairs, saturated or unsaturated rings. Furthermore, said radicals can contain halogen atoms, nitro, nitrile, sulfonic and relative ester groups, carbonyl, hydroxyl, carboxyl, thiol, amine and ether groups .
• the olefins can carry the above substituents both on unsaturated carbon atoms and in different positions.
• Non-limiting examples of olefins having formula (I) are: ethylene, propylene, allyl chloride, allyl alcohol, butenes, pentenes, hexenes, heptenes, octene-1, 1- tridecene, mesityl oxide, isoprene, cyclo-octene, cyclo- hexene or bicyclic compounds such as norbornenes, pinenes, etc.
• the preferred olefin is propylene. Propylene with a purity of over 70% is generally used. The propylene is preferably available as a stream from steam cracking with a minimum purity of 96%, the remaining percentage consisting of propane and typical C 3 impurities.
• the quantity of hydrogen peroxide with respect to the olefin is not critical, but a molar ratio olefin/H 2 02 ranging from 10:1 to 1:10, preferably from 6:1 to 1:1, is preferably used.
• the epoxidation reaction can be carried out in one or more liquid solvents at epoxidation temperatures, compatible with hydrogen peroxide and capable of dissolving the olefin and olefin oxide produced.
• Solvents of a polar nature consisting of an alcohol or mixture of C ⁇ -C 4 alcohols or a mixture of said alcohols with water with a prevalent alcoholic content are typically used.
• a mixture with a prevalent alcoholic content refers to a mixture containing over 50% by weight of alcohol or mixture of alcohols.
• C ⁇ -C 4 alcohols methanol is preferred for the purposes of the invention.
• a mixture of methanol and water containing at least 70% by weight of methanol is preferred.
• the buffering agent is selected from ammonia, ammonium acetate, ammonium formiate or a system consisting of a ni- trogenated base and one of its salts with an organic or in- organic acid as described in Italian patent application MI
• the buffering agent is fed in continuous with one of the reagents streams fed to the epoxidation reactor, in such a quantity as to maintain the pH of the reaction mix- ture, measured under the operating conditions, at a value higher than 5, preferably ranging from 5.5 to 8.
• the epoxidation catalyst which can be used in the process of the present invention is selected from those generally known under the name of titanium silicalites .
• titanium-silicalites can be used, with an MFI structure, described in the patent U.S. 4,410,501, which also describes their structural characteristics.
• Titanium silicalites in which part of the titanium is substituted by other metals such as boron, aluminum, iron or gallium, can also be used. These substituted titanium silicalites and the methods for their preparation are de ⁇ scribed in European patent applications 226,257, 226,258 and 266, 825.
• Titanium silicalites with a MEL or intermediate MFI/MEL structure can also be used.
• Other titaniu -silicalites can be selected from beta zeolites containing titanium and having a BEA structure, described in Spanish patent 2,037,596, ZSM- 12 containing titanium and optionally aluminum, described in "Journal of Chemical Communications, 1992, page 745".
• the preferred catalyst according to the present invention is titanium-silicalite having general formula (II) :
• x represents a number ranging from 0.0001 to 0.04, preferably the value of x ranges from 0.01 to 0.025, and described, for example in patents U.S. 4.410,501, 4,824,976, 4,666,692, 4,656,016, 4,859,785, 4,937,216.
• the catalyst can be used in the form of powder, pellets, icrospheres, extruded or other convenient physical forms .
• ligand co.gel
• inert carrier inert carrier
• the inert carrier may typically consist of silica, alumina, silica-alumina, zeolites, activated carbon, and other materials well known in the state of the art.
• the quantity of catalyst used in the process of the present invention is not critical; it is selected however so as to allow epoxidation reaction to be completed in the shortest possible time.
• the quantity of catalyst is generally selected in relation to the various parameters, such as the reaction temperature, reactivity and concentration of the olefin, the concentration of hydrogen peroxide, type and composition of the solvent, catalytic activity and type of reactor or reaction system used.
• the quantity of catalyst typically ranges from 1 to 15% by weight with respect to the reaction mixture, preferably from 4 to 10% by weight.
• the temperature used in the process of the present invention generally ranges from 20 to 150°C, preferably from 40 to 100°C, from 55 to 90°C is particularly preferred.
• the operating pressure is such as to allow the olefin to be maintained in liquid phase at the temperature pre- selected for the reaction.
• the operating pressure is higher than atmospheric pressure when gaseous olefins are used.
• the reactor used in the epoxidation reaction can be any reactor suitable for operating in continuous and con- ducting the reaction in a system such as that described, obtaining an effective contact between the olefin, the liquid phase and catalyst kept in suspension.
• stirred reactors for example, stirred reactors, bubble reactors, gas- lift reactors with internal or external circulation or CSTR (Continuous Stirred Tank Reactors) or PFR (Plug Flow Reac- tors) , as described in the state of the art, are suitable for the purpose.
• CSTR Continuous Stirred Tank Reactors
• PFR Plug Flow Reac- tors
• the olefin charged this term referring to fresh olefin, recycled olefin or their mixtures, is fed to the reac- tion step under flow-rate control and in excess to maximize the conversion and selectivity to olefin oxide and maintain the reaction pressure.
• a mixture consisting of fresh olefin deriving from battery limits and recycled olefin is preferably fed.
• the fresh olefin can be purified in the distillation column C4.
• the reaction unit is made up of three reactors R1-R2-R3 of the CSTR type and isotherms.
• the reactors RI and R2 operate under substantially identical conditions, i.e. at a temperature of about 55- 75°C and a pressure of 13 bars, whereas the reactor R3, which acts as finishing reactor, i.e. with exhaustion of the hydrogen peroxide fed to the reactors Rl and R2, operates at a temperature of 79-90°C and a pressure of 8 bars.
• the overall oxidation reaction of the olefin is carried out in such a way as to have a concentration of H 2 0 2 of less than 100 ppm in the stream leaving the unit R3.
• the reaction selectivity with respect to hydrogen peroxide is 98% molar with a conversion of 96%
• in the third reactor there is a selec- tivity of 80% molar and a conversion of 95%.
• the flash columns substantially operate under the same operating conditions and discharge, at the head, streams in vapour phase essentially consisting of non-reacted olefin, olefin oxide, inert products, for example aliphatic hydrocarbons such as propane, and solvent vapours.
• the columns discharge streams in liquid phase with a differentiated composition, which for Cl and C2 are partly recycled to the respective synthesis reactors RI and R2.
• vapours at the head of columns C1-C2-C3 are fed to a distillation column C4 to recover the non-reacted olefin at the head.
• the latter is recycled to the synthesis of the olefin oxide after partial elimination of the inert products.
• the vapours coming from the vents of reactors R1-R2- R3, are also fed to the column C4.
• the temperature at the bottom of the column C4 must not exceed 80°C with residence times in the order of 1 minute; this is to avoid degradation of the olefin oxide.
• the stream at the tail of the column C3 is substantially without H 2 0 2 and essentially consists of solvent, water and reaction by-products.
• This stream is fed to a decomposition section of the residual hydrogen peroxide R4 ' consisting of one or more fixed bed tubular reactors arranged in series.
• the hydrogen peroxide decomposition reaction is exothermic and takes place in liquid phase at about 80-90°C, with a residence time ranging from 1 to 10 minutes, preferably from 2 to 5 minutes .
• catalysts used in the decomposition reaction consist of metals of group VIII or their oxides.
• the carriers are selected from those of the known art and indi- cated above.
• the mixture leaving R4 is fed to a phase separator V4 which separates the oxygen generated from the decomposition of the hydrogen peroxide and the dilution inert product, preferably nitrogen, charged downstream of the reactor R4 to maintain the solvent/oxygen mixture released in the flash column below the lower flammability limit.
• the solvent-oxygen-inert product mixture leaving YA is then condensed in two condensers in series to recover the solvent, whereas the non-condensable products (oxygen and inert product with traces of solvent) are discharged.
• the liquid phase leaving R4 and the liquid mixture leaving V4 are fed to the distillation column C6-A and treated as described above.
• the condensation heat recovered at the head of the column C6-A can be used to supply all the reboiling units present in the process.
• the pressure of the column is kept at a suitable value for this purpose.
• a liquid stream rich in olefin oxide is extracted from the bottom of the distillation column C4, and is sent to a purification section C5.
• the latter consists of two columns in series due to the high number of plates and separates, at the head, residual vapours still present (non-reacted olefin and inert gases) , at the bottom, a liquid stream containing solvent and olefin oxide (recycled to the distillation column C3) and, laterally, a liquid stream consisting of olefin oxide with a commercial purity (> 99.8%) .
• vapours extracted from the head of the purification column C5 may still contain significant quantities of olefin oxide and are recycled upstream of the distillation column C4.
• the epoxidation catalyst after 1000 hours, does not show any sign of deterioration and the productivity and reaction selectivity are high.
• FIG. 1 represents an illustrative but non-limiting embodiment.
• the olefin for example propylene
• the buffering agent is fed to the reactors R1-R2-R3 parallelly with lines (Tl) - (T2) - (T3)
• half of the recycled solvent with the hydrogen per- oxide (4) is fed to the reactor RI (4A) and the other half to R2 (4B) .
• the filtered liquid reaction product leaving the sec- ond reactor R2 is fed with line (9) to the second distillation column C2 from whose head the propylene oxide produced and non-reacted propylene (12) , in vapour phase, are recovered, and from the bottom, a liquid stream (13) still containing hydrogen peroxide, a part of (13) is fed to the re- actor R3 and the remaining stream (13A) is recycled to the 01 09076
• reactor R2 to dilute the hydrogen peroxide to the desired concentration.
• the filtered liquid reaction product leaving the second reactor R3 is fed with line (14) to the third distilla- tion column C3 from whose head the propylene oxide produced and non-reacted propylene (16) , in vapour phase, are recovered, and from the bottom, a liquid stream (15) still containing hydrogen peroxide, fed to the reactor system R4 (the system R4 refers to the reactor R4 itself, a phase separator V4 and two condensers in series E421/E422 on the vapour phase leaving V4) .
• the liquid reaction product leaving the system R4 is fed to the column C6-A (18), the gaseous product vented into the atmosphere containing oxygen, nitrogen and traces of methanol is represented by line (17) .
• the diluting nitrogen is fed to the system R4 with line (AZ) .
• the liquid product leaving the reactor system R4, without hydrogen peroxide and essentially consisting of solvent, water and by-products, is fed with line (18) to the solvent recovery section consisting in this particular case of a series of distillation columns C6 A-B-C. Water and the reaction by-products (24) are discharged from the bottom of C6-A. At the head of C6-A, the solvent (23) is recovered and sent to the column C6-B. At about 2/3 of the height of C6-A an acid solution (Al) is fed, which blocks the nitrogenated compounds present in vapour phase.
• the head of the column C6-B consisting of light compounds (methyl formiate, dimethoxymethane) present in the methanol at the inlet of C6-A, at a concentration of 1-2% by weight of methanol, is fed to the column C6-C.
• the light concentrated products (6-8% by weight) leave the head of the column C6-C with the flushing stream (31) .
• the bottom products of columns C6-B and C6-C when joined (33) form the r ⁇ etha- nol recycled to the synthesis reaction of hydrogen peroxide.
• the propylene is separated at the head of the column C4 together with the inert products (27) + (25) .
• the inert products, such as propane, are inserted into the cy- cle together with fresh propylene (5) .
• a stream rich in propylene oxide (28) is recovered at the bottom of the column C4 and is fed to the purification section of propylene oxide, in this particular case consisting of a distillation column C5 (in two sections) .
• a stream in vapour phase (29) still containing traces of non- reacted propylene and propylene oxide is recovered at the head of the column C5; this stream is recycled by means of the compressor Kl to the column C4.
• a liquid stream (26) containing propylene oxide and solvent is extracted from the bottom of the column C5 and is sent back to the column C3.
• the propylene oxide with a commercial purity is extracted from the column C5 as a lateral cut (30) .
• the stream of distilled methanol (33) coming from the propylene oxide synthesis section goes to the hydrogen per- oxide synthesis section.
• a stream (35) of an aqueous solution of HBr (halogenated promoter) and a stream (36) of an aqueous solution of H 2 S0 4 (acid promoter) are added to the stream (33) ; the pump PI sends the mixture obtained (37) to the hydrogen peroxide synthesis reactor R5 at a pressure of 100 bars.
• the streams (39) - (40) - (41) of hydrogen, oxygen and nitrogen, respectively, are sent by means of the compressor K2 to the reactor R5 at 100 bars.
• the ventilator K3 recycles the non-reacted gases from the top of the reactor into the reaction medium.
• the vapour phase leaving FI, after condensation (45) feeds the separation col- u n C7 fed at the head with water (48) .
• the gases at the head C7 (46) are flushed from the cycle, the stream (47) at the bottom of the column C7 containing traces of methanol and water is sent to a biological treatment system.
• the gases of the top of the reactor removed for analysis with the on-line analyzer An, are also sent to the flash column FI.
• the liquid stream (4) leaving FI consists of hydrogen peroxide (7% weight), water and methanol. Said stream forms the feeding stream to the propylene oxide synthesis.
• the process described above allows epoxides to be obtained with a high productivity over a period of time and a high selectivity, using a method which can be easily applied on an industrial scale and with the possibility of operating in continuous.
• the following operative example is provided for illustrative purposes and does not limit the scope of the invention.
• the titanium silicalite catalyst of the type de- scribed in patent U.S. 4,937,216, is present in the reac- tors RI, R2 and R3 in a concentration of 6% by weight with respect to the slurry.
• the catalyst bed of the decomposer R4 in pellets with an active phase of 15%, is charged in volume excess to guarantee exhaustion of the hydrogen peroxide.
• the heterogeneous catalyst based on palladium and platinum is kept in dispersion in the liquid reaction medium at 1% by weight in R5.
• Table 1 enclosed (3 pages) indicates the balances and composition of the single streams.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Epoxy Compounds (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Oxygen, Ozone, And Oxides In General (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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